Patent GB-844328-A (GB)
Title: Improvements in or relating to photographic cameras
IPC: G03B7/12
Filed: 1958-02-20
Abstract: 844,328. Photo-electric control of photographic exposure. DECKEL, H., and DECKEL, F. W. Feb. 20, 1958 [Feb. 22, 1957], No. 5623/58. Class 40(3). [Also in Group XX] A camera has setting members for the diaphragm aperture and shutter speed and a built-in photo-electric exposure meter operating a pointer movable over a contact bank and adapted to be clamped to one of the contacts, one setting member having means for varying the photo-cell current and the other member carrying a wiper electrically connected to a source of current through the coil of an electromagnet and which sweeps a second contact bank connected to the first bank so that the second setting member acts as a selector switch for completing the energizing circuit of the magnet coil through the contact which has been engaged by the pointer, an arresting member operable on energization of the magnet being located at a fixed point and adapted to arrest the second setting member. As shown, on loading the camera with fresh film, a film speed ring 90 is first adjusted relative to a shutter speed setting ring 28 ; upon actuation of a cocking lever 12, a diaphragm control ring 40 is rotated by means of linkage gears to a full aperture position where it is held by a catch 48, and at the same time the film is wound on a frame. Focusing is achieved by the ring 26 and a shutter speed is selected by means of the ring 28 which has a scale 30 co-operating with a lock 32. A photo-cell 18 energizes a moving coil device 20 to move a pointer 22 over a scale 88 ; the extent of deflection is governed primarily by the amount of light incident on the photo-cell, but the resulting current is varied by movement of the shutter speed setting ring 28 which alters the setting of a potential divider comprising a resistance wire 100, a fixed contact 102 which leads to the wire 106a via a slip ring 104 and a contact 106, and variable contacts 108, 110 which correspond to different photo-cell ranges. On depression of a button 16, one of a set of studs 82 I-VII becomes connected to a source of current by contact with the needle 22 and at the same time the catch 48 is tripped to release the diaphragm setting ring 40 which begins to rotate under spring force. When a contact 80 of the ring 40 engages one of the studs 82 to complete the contact through the pointer 22 an electromagnet 74 is actuated to release a pin 64 normally held inoperative by a permanent magnet 72 - which moves inwards to engage one of the notches 45 on the ring 40 to hold the diaphragm at the correct position according to the light value. When this point has been reached the shutter release is actuated. In a modification, a further ring which trips the shutter release rotates with the ring 40 but is retarded by an escapement mechanism; if the shutter is set to a value to which there is no corresponding stop value, the ring 40 will move to the end of the path without being contacted by the pin 64; in this case it triggers a latch at the end of its path which prevents the retarded ring from reaching the position at which it causes exposure. For fresh exposures, the potential divided is further influenced by the focusing ring.